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netmap: fix txsync check in netmap poll

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To check if txsync can be skipped, it is necessary to look for
unseen TX space. However, this means comparing ring->cur
against ring->tail, rather than ring->head against ring->tail
(like nm_ring_empty() does).
This change also adds some more comments to explain the optimization
performed at the beginning of netmap_poll().

MFC after:	3 days
Sponsored by:	Sunny Valley Networks
This commit is contained in:
Vincenzo Maffione 2018-12-22 16:23:42 +00:00
parent e1ed1fbdea
commit 58e185425a
1 changed files with 18 additions and 11 deletions
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29
sys/dev/netmap/netmap.c
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@ -3292,31 +3292,38 @@ netmap_poll(struct netmap_priv_d *priv, int events, NM_SELRECORD_T *sr)
* that we must call nm_os_selrecord() unconditionally.
*/
if (want_tx) {
enum txrx t = NR_TX;
for (i = priv->np_qfirst[t]; want[t] && i < priv->np_qlast[t]; i++) {
const enum txrx t = NR_TX;
for (i = priv->np_qfirst[t]; i < priv->np_qlast[t]; i++) {
kring = NMR(na, t)[i];
/* XXX compare ring->cur and kring->tail */
if (!nm_ring_empty(kring->ring)) {
if (kring->ring->cur != kring->ring->tail) {
/* Some unseen TX space is available, so what
* we don't need to run txsync. */
revents |= want[t];
want[t] = 0; /* also breaks the loop */
want[t] = 0;
break;
}
}
}
if (want_rx) {
enum txrx t = NR_RX;
const enum txrx t = NR_RX;
int rxsync_needed = 0;
/* look for a reason to run the handlers */
for (i = priv->np_qfirst[t]; i < priv->np_qlast[t]; i++) {
kring = NMR(na, t)[i];
if (kring->ring->cur == kring->ring->tail /* try fetch new buffers */
|| kring->rhead != kring->ring->head /* release buffers */) {
if (kring->ring->cur == kring->ring->tail
|| kring->rhead != kring->ring->head) {
/* There are no unseen packets on this ring,
* or there are some buffers to be returned
* to the netmap port. We therefore go ahead
* and run rxsync. */
rxsync_needed = 1;
break;
}
}
if (!rxsync_needed)
revents |= want_rx; /* we have data */
if (!rxsync_needed) {
revents |= want_rx;
want_rx = 0;
}
}
#endif